1. Field of the Invention
This invention relates to an antenna for transmission and receipt of RF signals on a hand-held, portable cellular phone and in particular, to an improved antenna having reactance cancellation for improved antenna efficiency, improving the transmission and receipt signal efficiency, and reducing or eliminating the RF field immediately in contact with the cellular phone user.
2. Description of the Prior Art
Cellular telephones operating in the 800 to 1900 megacycle RF frequency range are well known in the art. More specifically cellular communication may occur in frequency ranges including 824-924 MHz, 1750-1870 MHz, 1750-1780 MHz, 1840-1870 MHz and other high frequency ranges which are being developed. In recent years, hand-held, portable cellular phones in these and other ranges have become quite common. However, problems which continue to exist include inadequate efficiency in signal transmission and signal radiation around and through the phone user at levels which have adverse health results. One deficiency in current hand-held, portable telephones is that numerous cell sites are required because of the limited range of each unit. Such hand-held cellular phone units also exhibit from time to time breakup and distortion in the signal receipt or transmission, and often, certain locations do not permit their use because of the total signal shadow. Cellular phones also radiate an RF wave pattern that typically includes a ground wave or negative signal that is transmitted around and through the user while the hand-held phone is in use; that is, while the phone unit is held to a person's ear to allow the person to hear or to talk while the device is radiating. A milligauss electromagnetic field detecting unit can be used around a cellular phone in use to show certain electromagnetic radiation patterns that are in contact with certain areas of the user's head and upper torso.
Typically, cellular phones use a Marconi-type antenna which has positive and negative wave patterns that include a ground wave. Conventional antennas are typically current-fed, two-element systems that use the phone case as a counterpoise or ground plane to help achieve impedance matching with the 50 ohm output impedance of the phone. Current fed systems normally comprise a parallel LC reactance circuit, having adjustable inductance, connected to a phone output. Examples of these antenna systems may be found in U.S. Pat. Nos. 3,474,453 issued to Ireland; 4,238,799 issued to Parfitt; 2,648,771 issued to Cork; 4,730,195 issued to Phillips, et al; 4,940,989 issued to Austin; 5,214,434 issued to Hsu; 5,214,437 issued to Hensler; and 3,155,751 issued to Roll, and German reference issued Nov. 4, 1981 to Koehler. As can be seen by Ireland and Koehler, the capacitor is typically connected electrically in parallel to the inductance by making a direct conductive link.
It is known that the impedance at the center of a conventional antenna is approximately 72 ohms, and that for maximum efficiency, the impedance of the phone should match the impedance of the signal output device. Thus, although the impedance at the center of a conventional antenna is approximately 72 ohms, the impedance approaches 50 ohms when the phone is hand-held because of the natural capacitance in one's body. Accordingly, RF wave energy is transmitted around and through the user's body. Recent studies show that this can be harmful to the user.
Experimental results suggests that AC electric and magnetic fields increase the risk of certain cancers and other physiological and psychological harms. Radiated signals from a cellular phone antenna surround the body with an electromagnetic field that can produce adverse results in the body. Based on recent studies, these fields are produced by cellular phone antennas which are typically current fed Marconi systems, as noted, that use the phone output as a ground return such that only 50% of the signal is transmitted away from the antenna. Current fed antennas comprise quarter-wave (1/4 wavelength) antennas to match 1/4 wavelength systems in conventional phones. In contrast, voltage fed antennas comprise 1/2 wavelength antennas which are capable of approaching full signal transmission, i.e. 100%, so as to limit or substantially eliminate a cellular phone user's exposure to that portion of signal typically left behind in quarter-wave antennas. The problem is that an antenna can not be voltage fed unless it is 1/2 wavelength and a 1/2 wavelength antenna can not be connected to a current fed 1/4 wavelength system. Since conventional phones are 1/4 wavelength current fed systems, 1/2 wavelength antennas can not be effectively used.
While the elimination of counterpoise has been addressed in the background art, the problems noted above have not been fully addressed. For instance, U.S. Pat. No. 3,474,453, issued Oct. 21, 1969 to F. E. Ireland, Applicant herein, shows a whip antenna with adjustable tuning that could be used to eliminate problems with the earth or surrounding structures for transmission purposes. U.S. Pat. No. 4,584,587, issued Apr. 22, 1986 to F. E. Ireland, Applicant herein, shows a tunable antenna with coupling at the input that can be used without a counterpoise.
It is desirous to improve cellular phone signal transmission to reduce the adverse affects of signal generated fields and one way to increase signal transmission efficiency would be to provide a 1/2 wavelength antenna that is operable in a 1/4 wavelength cellular system. Therefore, there exists a need for an antenna system that is able to achieve antenna efficiency through impedance matching without radiating the actual user. The present invention overcomes problems in the prior art by providing an improved antenna having more efficient RF signal radiation transmission and receipt. The antenna system is used with a hand-held, portable cellular phone to increase signal efficiency, both in transmission and receipt distance range, to eliminate ground distortion or building structure distortion through improved signal efficiency, and to eliminate RF radiation patterns associated with ground waves from the body areas of the user of a hand-held, portable cellular telephone. The instant invention accomplishes its results with an antenna system that converts a 1/4 wavelength system into a 1/2 wavelength system using reactance cancellation.